The goal of this program is to reduce the occurrence of stroke. This leading cause of disability, and third leading cause of death, strikes without warning in 80% of cases;finding and correcting the conditions that lead to stroke can prevent stroke. At least 50% of strokes arise from plaque at the carotid bifurcation. Removing plaque (a "carotid endarterectomy") from asymptomatic patients who have significant carotid stenoses reduces their stroke rate over the next five years by a factor of almost three. This is an excellent way of reducing the occurrence of stroke. Unfortunately, screening to find this significant plaque before it causes stroke, using conventional, general-purpose duplex Doppler ultrasound instruments, is too expensive to justify;these ultrasound instruments require a skilled sonographer and skilled physician to be effective. Realization of a special-purpose ultrasound instrument, specifically designed for carotid screening and meant for use in primary-care offices as a quick and inexpensive means of finding carotid stenoses and directing them to specialists to correct, is our aim. In the "proof-of-concept" Phase I of this SBIR we developed and built such as special purpose instrument, and showed that it had high sensitivity and specificity for finding significant carotid stenoses. The examinations required only a few minutes, nonspecialists learned to use the instrument quickly, and the cost of the instrument was only a few thousand dollars. In Phase II, a pilot study of such screening is proposed. Using an improved version of the Phase I instrument, four to six primary care physician offices will be equipped with the carotid screening system and nurses instructed in its use. Physicians will invite appropriate patients, those aged 60+ with at least one additional risk factor, to be screened with the device, and those found with carotid stenoses will be directed to a central certified non-invasive vascular laboratory for conventional duplex Doppler examination. The data from 1400 patients, calculated as the number required for statistical significance, will show whether this two-step screening system is (or is not) cost-effective;the cost-effectiveness will be determined by a Markov model appropriate to this screening that will be developed as part of this research.